Millimeter phased array



Oct 1966 L. L. BLAISDELL 3,277,489

MILLIMETER PHASED ARRAY Filed Sept. 50, 1963 5 Sheets-Sheet l FIG. 1A

IFIG.1B IFIG. 1C

INVENTOR. LEONARD L. BLA/SDELL ATTORNEY.

Oct. 4, 1966 L. L. BLAISDELL 3,277,489

MILLIMETER PHASED ARRAY Filed Sept. 30 1963 3 Sheets-Sheet 2 INVENTOR.LEONARD L. BLAISDEL L ATTORNEY.

Oct. 4, 1966 L. L. BLAISDELL 3,277,489

MILLIMETER PHASED. ARRAY Filed Sept. 50, 1963 5 Sheets-Sheet 5 RELATIVEPOWER (d b) ANGLE FROM ARRAY NORMAL (DEGREES) INVENTOR. LEONARD LBLAISDELL ATTORNEY.

Unite 3,277,489 Patented Oct. 4, 1966 3,277,489 MILLIMETER PHASED ARRAYLeonard L. Blaisdeil, Mcdway, Mass, assignor to Sylvania ElectricProducts Inc, a corporation of Delaware Filed Sept. 30, 1963, Ser. No.312,733 4- Claims. (Cl. 343-777) This invention relates to antennas andmore particularly to electronically steerable antennas which areespecially suited for operation in the millimeter wavelength region.

Phased array antennas for communications and radar are well known andhave gained prominence in recent years since they provide rapid,accurate, inertialess beam steering. The accuracy of these arrays, as isthe accuracy of all antenna systems, is ultimately limited by thefrequency at which the antenna system operates. In order to obtainhigher resolution, higher operating frequencies must be used; however,at extremely highv frequencies, for example, in the millimeterwavelength region above gigacycles per second (gc.), antennasconstructed by known microwave techniques are difficult and costly tobuild due to the small physical dimensions of microwave components atthese frequencies, and the dimensional accuracy required. It is,therefore, an object of the present invention to provide an efficient,relatively simple, extremely accurate phased array particularly suitedfor operation in the millimeter wavelength region. Such an array wouldhave specific application, for example, in space vehicles.

Another object of the invention is to provide a phased array having afeed structure integral with the antenna elements.

Another object of the invention is to provide an antenna array which isfabricated in a single integral member.

Still another object of the invention is to provide a phased arrayhaving improved radiating elements at millimeter wavelengths.

A further object of the invention is to provide a phased array in whichphase shifters are incorporated into the radiating elements.

Briefly, the invention comprises a phased array in which the radiatingelements are field-constrained parallel plate waveguides whereinradiation is concentrated at discrete locations within a single pair ofground planes. Typical examples of such waveguide are H-guide, ridgeguide, or a pair of confronting grooves cut in a respective pair ofground planes. Power division between the elements of the array isprovided by a power divider/combiner which may be integral with theantenna elements, and which supplies energy from an energy source to therespective antenna elements when the array is operating in thetransmitting mode, or which combines energy received by the respectiveantenna elements when the array is operating in the receiving mode.Suitable phase shifters are provided in each antenna element to producethe requisite phase shift to appropriately steer the antenna beam.

The foregoing, together with other objects, features, and advantages ofthe present invention will be more apparent from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIGS. 1A, 1B and 1C are elevation views of three fieldconstrainedparallel plate waveguide useful in the present invention;

FIG. 2 is a pictorial view of a dielectric power divider and multipleradiating elements constructed in accordance with the invention;

FIG. 3 is a pictorial view of one embodiment of the present invention;

FIG. 4 is a partly cut away pictorial view of another embodiment of theinvention;

FIG. 5 is a partly cut away pictorial view of a further embodiment ofthe invention; and

FIG. 6 is the measured antenna pattern of a phased array constructed inaccordance with the invention.

Referring to FIGS. 1A, 1B, and 10 there are shown three electricallyequivalent types of field-constrained parallel plate waveguide. Thedielectric loaded waveguide, or H-g'uide shown in FIG. 1A comprises adielectric slab 10 of rectangular cross section, disposed between a pairof parallel ground planes 12a and 14a with its long axis at right anglesthereto. The groove guide illustrated in FIG. 1B comprises a pair ofparallel ground planes 12b and 14b having confronting grooves and 82,respectively, cut in each ground plane. The ridge guide shown in FIG. 1Ccomprises a ground plane having a ridge 84 formed thereon and facing alike ridge 86 formed on a second ground plane 140. In the case of theH-guide, it is well known that radiation between the ground planes canbe confined to the region within and immediately adjacent dielectricslab 10 by proper choice of a dielectric material having a suitabledielectric constant and slab thickness. Radiation in a groove guide andin a ridge guide can be confined to the region between the grooves orridges by suitably dimensioning the width and depth of the grooves orridges, as the case may be. Since radiation within the waveguide isconfined to discrete regions, no side walls are needed to preventradiation from the edges of the guide. Side walls can, of course, beprovided to satisfy mechanical considerations, although electrically,the waveguide functions equally as well with or without them. Aplurality of dielectric slabs, confronting grooves, or ridges can,therefore, be arranged side by side between a pair of ground planes andcan be suitably energized to function as an antenna array.

The construction of an H-guide array, with the ground planes removed forclarity, is shown in FIG. 2, and in cludes a tapered dielectric member16 which is shaped at one end to form fingers or radiating elements 18,20, 22, and 24. Of course, more or less than four radiating elements canbe provided to suit the intended requirement. Tapered sections 34, 36,38, and 40 between the tapered section 16 and the fingers provideimpedance matching to prevent unwanted energy reflection from theradiating elements. The dimensions of the tapered sections are chosen tosuit the frequency of operation. Slots 26, 28, 30, and 32 are cut inelements 18, 20, 22, and 24, respectively, near the outer end thereof,to accommodate phase shifting slugs, one of which is shown removed fromthe slot in FIG. 2, and designated by reference numeral 48. The slugsare shown in their operative position in FIG. 3. Tapered member 16functions as a dielectric power divider and provides an expedient meansof launching the desired energy mode from an energy source, and alsoprovides a simple means of adjusting the illumination taper across theelements of the array by suitably apportioning selected amounts ofenergy to the several radiating elements. It is evident that powerdivider 16 and elements 18, 20, 22, and 24 can be fabricated as a singleunit, such as by well known molding or milling techniques. The majorportion of the array, therefore, can be economically and accuratelyconstructed in a single integral piece.

The complete array embodying the dielectric structure of FIG. 2, isillustrated in FIG. 3. The dielectric power divider and radiatingelements are enclosed in a housing 42, which, for example, may befabricated from epoxy resin with ground planes 44 and 46 disposed on theupper and lower inside faces thereof, respectively. Alternatively,housing 42 may be fabricated of copper or other conductive material.Since electrical performance of the array is unaffected by .the presenceor absence of conductive side walls, it makes no difference whether ornot the ground planes are insulated from each other. Dielectric slugs48, 50, 52, and 54 are slidably mounted in slots 26, 28, 30, and 32,respectively, in the dielectric member, extending through suitable holes72 provided on one face of housing 42. A suitable mechanism,schematically indicated at 56, is provided to move the slugs in or outof the slots to vary the phase of signals in the radiating elements, asthe situation requires. Dielectric slugs 48, 50, 52, and 54 have acurved lower surface as shown in FIG. 2, to provide impedance matching.Other suitable impedance matching configurations may, of course, be usedequally as well.

A section of rectangular waveguide 58, and a mounting flange 60 areconnected at the apex end of the power divider to couple energy from anenergy source to the array, if the array is used for transmitting; or,if the array is used for receiving, to couple received energy toappropriate signal utilization means.

The operation of the array will be described in the transmitting mode,it being understood, however, that it is a reciprocal device and can beused equally well in the receiving mode. In operation, a signal from anenergy source is applied to the input terminal of the array by any wellknown means, for example by means of Waveguide 58. Energy propagatesthrough power divider 16 and is divided among radiating elements 18, 20,22, and 24, which radiate the energy into space. The electrical lengthof the radiating elements, and thus the phase of signals propagatingtherethrough, is dependent upon the distance that slugs 48, 50, 52, and54 are inserted into their respective radiating elements. The electricalpath length through the radiating elements increases with the depth ofinsertion of the slugs; consequently, the change in the phase of asignal propagating through elements 18, 20, 22, and 24 can be adjustedto steer the antenna beam in any desired direction. The differentialphase shift, which determines the angular extent the beam moves awayfrom its zero scan reference position, depends upon the dimensions anddielectric constant of the dielectric slugs.

Another embodiment of the invention is suggested by remembering that apair of confronting grooves cut in opposite surfaces of a pair of groundplanes is electrically equivalent to an H-guide. As shown in FIG. 4, aplurality of radiating elements can thus be provided by simply cuttingsuitable grooves in a pair of confronting ground planes; power divisionis provided by cut-ting a grooved structure of the same shape as thetapered dielectric power divider 16 of FIG. 2. More specifically,tapered groove 90 formed in the lower face of metal housing 62, isdivided into groove 64, 66, 68, and 70. A similar configuration ofgrooves is provided on the upper face, only grooves 64 and 66 beingvisible in the figure. The energy is constrained in the region betweenpairs of confronting grooves by suitably dimensioning the groove widthand depth. Slots 72:: are provided in the upper face of housing 62 toaccommodate phase shifting slugs, as in the embodiment of FIG. 3. Theslots are disposed such that the slugs extend into the region betweenconfronting grooves where the energy is confined. Since the wavepropagation occurs in air rather than in a solid dielectric material,this embodiment has lower dielectric loss than an embodiment of the typeshown in FIG. 3, and is therefore, electrically more efficient.

The operation of the array shown in FIG. 4 is identical to that of thearray of FIG. 3. Energy is applied to the input by means of flange 60aand waveguide section 58a, and is guided by the groove power dividerformed by groove 90 and its counterpart on the upper face of housing 62,to the radiating elements consisting of grooves 64, 66, 68, and 70 andtheir confronting counterparts, only two of which, 64' and 66', areillustrated. Dielectric slugs (not shown) are slidably mounted inrespective slots 72a, as in the embodiment of FIG. 3, to alter the phaseof signals propagating in the region of the confronting groves tothereby steer the antenna beam.

A further electrically equivalent embodiment of the invention can bemade using ridge guide, such as that illustrated in FIG. 10. As shown inFIG. 5, a plurality of ridges 100, 102, 104, and 106 are formed in thelower face of metal housing 104, and a like plurality of ridges areformed on the upper face, only ridges 'and 102' being visible in thefigure. A tapered ridge 106 formed in the lower face of housing 104, anda similar tapered ridge provided in the upper face, comprise the powerdivider. Slots 72b are provided in the upper face of housing 104 toaccommodate phase shifting slugs, as in the embodiments of FIG. 3 andFIG. 4.

The operation of this embodiment is identical to that of the previousembodiments. Energy is applied to the input by means of flange 60b andwaveguide section 5812, and is guided by the power divider formed byridge 106 and its counterpart on the upper face of housing 104, to theradiating elements consisting of ridges 100, 102, 104, and 106 and theirconfronting counter-pants. As in the previously discussed embodiments,the phase of signals propagating in the region of the confronting ridgesis altered 'by dielectric slugs (not shown) slidably mounted inrespective slots 72b provided in the upper face of housing 104.

In a four element array, of the type illustrated in FIG. 3, constructedfor operation at 45 go, the power divider, radiating elements, and phaseshifting slugs were fabricated of titanium dioxide-loaded polystyrenehaving a dielectric constant of 9. The radiating elements were .06 inchwide, .117 inch high, and the spacing between elements, as measuredbetween element centers, was .17 inch. The overall dimensions of thearray were 4 inches long, 1.25 inches wide, and .25 inch high. A maximumphase shift of 85 degrees was obtainable in each radiating element bymoving the appropriate dielectric slug in or out of the correspondingradiating element. For a phase shift of 85 degrees, the calculated beamsteering angle for the array geometry here under consideration is 7degrees. This calculated beam steering angle was demonstratedexperimentally, as shown by the antenna pattern of FIG. 6. Referring toFIG. 6, curve 110 is the measured antenna pattern when the antenna beamis steered to its :maximum right-hand position, while curve 112 is themeasured antenna pattern when the beam is steered .to its maximumleft-hand position. It is seen that the antenna beam is steerable up toan angle of approximately 7 degrees on either side of the array normal,or a total steering angle of approximately 14 degrees. Greater steeringangles can, of course, be obtained by providing greater phase shifts inthe antenna elements, and by suitable geometric design of the array.

From the foregoing, it is seen that a simple, compact, easilyconstructed phased array has been provided which is particularly suitedfor operation in the millimeter wavelength region.

While there have been described what are now thought to be preferredembodiments of the present invention, various modifications andalternative constructions will now occur to those skilled in the artwithout departing from the true scope of the invention. For example,electronically controlled phase shifters, such as those employingferroelectric material may be inserted into each radiating element, andby applying appropriate control voltages across respective elements, thedielectric constant of the ferroelectric material, and hence the phaseshift of signals through the radiating elements can be selectivelychanged to steer the antenna beam. Accordingly, it is not intended tolimit the scope of the invention by what has been specifically shown anddescribed except as indicated in the appended claims.

What is claimed is:

1. A phased array comprising a dielectric member disposed between and incontact with a pair of ground planes, said member having an apex endwhich outwardly tapers to a predetermined width, at which point itdivides into a plurality of fingers parallel to each other, each of saidfingers having a slot cut therein, a like plurality of dielectric slugseach slidably mounted in a corresponding one of said slots, and meansfor moving said slugs in or out of said slots to thereby selectivelyalter the phase of signals propagating in the region of said fingers.

2. A phased array comprising a first and a second ground plane having apair of confronting surfaces each surface having a field constrainingelement therein, said element having an apex end which outwardly tapersto a predetermined width, at which point it divides into a plurality ofelongated field constraining elements parallel to each other, thetapered element and elongated elements of one ground plane confrontingcorresponding elements of the other ground plane, one of said groundplanes having a plurality of slots therein with a slot oommunicatingwith each pair of respective elongated confronting elements, a likeplurality of dielectric slugs each slidably mounted in a correspondingone of said References Cited by the Examiner UNITED STATES PATENTS2,959,784 11/1960 Pierce 343783 3,041,605 6/1962 Goodwin et al. 343-854OTHER REFERENCES Tisher, F. 1.: Properties of the H-Guide at Microwavesand Millimeter Waves, IRE Wescon Convention Record, 1958, vol. 2, Pt. I,pages 4-12.

HERMAN KARL SAALBACH, Primary Examiner.

M. NUSSBAUM, A. R. MORGANSTERN,

Assistant Examiners.

2. A PHASED ARRAY COMPRISING A FIRST AND A SECOND GROUND PLANE HAVING APAIR OF CONFRONTING SURFACES EACH SURFACE HAVING A FIELD CONSTRAININGELEMENT THEREIN, SAID ELEMENT HAVING AN APEX END WHICH OUTWARDLY TAPERSTO A PREDETERMINED WIDTH, AT WHICH POINT IT DIVIDES INTO A PLURALITY OFELONGATED FIELD CONSTRAINING ELEMENTS PARALLEL TO EACH OTHER, THETAPERED ELEMENT AND ELONGATED ELEMENTS OF ONE GROUND PLANE CONFRONTINGCORRESPONDING ELEMENTS OF THE OTHER GROUND PLANE, ONE OF SAID GROUNDPLANES HAVING A PLURALITY OF SLOTS THEREIN WITH A SLOT CONMUNICATINGWITH EACH PAIR OF RESPECTIVE ELONGATED CONFRONTING ELEMENTS, A LIKEPLURALITY OF DIELECTRIC SLUGS EACH SLIDABLY MOUNTED IN A CORRESPONDINGONE OF SAID SLOTS, AND MEANS FOR MOVING SAID SLUGS IN OR OUT OF SAIDSLOTS TO SELECTIVELY ALTER THE PHASE OF SIGNALS PROPAGATING IN THEREGION OF SAID CONFRONTING ELONGATED ELEMENTS.